The long-term goal of the proposed research is to develop methods to measure and counteract the stresses developed in resin-based materials due to polymerization shrinkage. The specific aims are: (i) to build a tensometer for measuring stresses developed during the polymerization of resin-based materials; (ii) to investigate the potential relaxation of polymerization stresses in resins and composites. An apparatus for measuring shrinkage stresses will be built following a design by Feilzer et al., (1993). Slow and fast curing composite systems with increasing amounts of fillers, will be used to test a possible correlation between stress and shrinkage and to evaluate instrument reproducibility. Stoichiometric amounts of compounds will be added to composites to compensate for curing contraction. If these amounts will not reduce stress to zero, compound concentrations will be increased to further reduce stress. The limiting amounts will be determined from the effects of the reactant concentrations on other physical properties of the composite (e.g., degree of cure, diametral tensile strength, 4-point transverse test (TS), adhesion to dentin, water sorption and solubility). To maintain high physical properties, a decrease in TS of more than 15% would be considered unacceptable. Systems identified in Specific Aims as candidate systems for reducing polymerization-induced shrinkage and stress in dental composites will be compared in a final randomized side- by-side experimental design including controls. Although stress reduction will be the primary response variable of interest, shrinkage, degree of cure, DTS, transverse strength, water sorption and solubility will all be considered in the final recommendation of a useful system.